JP2011034071A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display device having an LED backlight light source, in which electrical power consumption associated with turning on an LED is reduced when the luminance is controlled according to the image quality through a combination of pulse-width modulation (PWM) and a current control system. <P>SOLUTION: In the LED backlight 10, the light emitting luminance of the LED is controlled by both of a PWM system, which modifies a duty that indicates the per-cycle lighting time of a pulse, which turns the LED on/off, and a current control system, which selects the value of the current supplied to the LED from a plurality of set values. At least one of the plurality of set values is a predetermined current value at which duty reaches a maximum value at the maximum luminance value used in a specified image quality mode of the image quality modes established in the liquid crystal display device 1. In the specified image quality mode, the greatest luminance value used is smaller than at least the greatest luminance value used in other specified image quality modes. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device including a liquid crystal panel and a light source of a light emitting diode that irradiates the liquid crystal panel.

  In recent years, energy saving has been emphasized, and reduction of power consumption has become an important theme in a liquid crystal display having a liquid crystal panel.

  In liquid crystal display devices, products using a light source of a light emitting diode (LED) as a backlight are on the market.

  As the light emission luminance adjustment method of the LED backlight, there are a pulse width modulation (PWM) method and a current value control method. Since the PWM method is time control, fine control with high control accuracy is possible. On the other hand, the current value control method has higher power efficiency than the PWM method, but it is not suitable for delicate control because the control width cannot be made fine like the PWM method and correction is necessary for linear control. Yes, it becomes step-by-step control.

  Patent Document 1 discloses a backlight that controls R, G, and B backlights by supplying R, G, and B drive currents and R, G, and B PWM signals to an LED backlight unit. A liquid crystal display device including a drive unit and a timing controller that controls operations of a scan driver, a source driver, and a backlight drive unit is disclosed.

JP 2006-235565 A

  However, in the conventional LED backlight including the technique described in Patent Document 1, it is only possible to perform luminance control using the PWM method and luminance control using the current value control method. Therefore, when displaying an image after being incorporated as a product, it is preferable to specifically control the brightness by combining the two in order to provide an image quality suitable for viewing and reduce power consumption. It is not considered whether it is preferable above. Therefore, there is a need for a clear mechanism for how to combine both luminance controls when mounting them in a product.

  The present invention has been made in view of the above-described circumstances, and an object thereof is to meet the image quality by combining the PWM method and the current value control method in a liquid crystal display device including an LED backlight light source. In controlling the brightness, the power consumption for lighting the LED can be reduced.

  In order to solve the above-described problems, a first technical means of the present invention includes a liquid crystal panel that displays an input video signal, a light source of a light emitting diode that illuminates the liquid crystal panel, and light emission that controls the light emission luminance of the light emitting diode. In the liquid crystal display device having a luminance control unit, the light emission luminance control unit includes a pulse width modulation method for changing a duty indicating a lighting time per cycle in a pulse for turning on / off the light emitting diode, and the light emitting diode. And a current value control method for selecting a current value to flow from a plurality of set values, and controlling the light emission luminance of the light emitting diode, and at least one of the plurality of set values is set in the liquid crystal display device The maximum luminance value used in a specific image quality mode among the image quality modes being used, and the predetermined current value at which the duty is the maximum value. Image quality mode, the maximum luminance value to be used is obtained by being a less quality mode than the maximum luminance value to be used in at least certain other image quality mode.

  According to a second technical means, in the first technical means, the specific image quality mode is an image quality mode provided as a mode most used by a user.

  According to a third technical means, in the first or second technical means, the light emission luminance control unit needs to be changed to a luminance value exceeding the maximum luminance value during operation in the specific image quality mode. Is controlled using a current value used in the other specific image quality mode.

  According to a fourth technical means, in the third technical means, when the light emission luminance control unit needs to be changed to a luminance value lower than the maximum luminance value during operation in the other specific image quality mode. The control is performed using a current value used in the specific image quality mode.

  According to a fifth technical means, in the third or fourth technical means, the light emission luminance control unit gradually changes the current value and the duty simultaneously when changing the current value. is there.

  According to the present invention, in a liquid crystal display device equipped with an LED backlight light source, the power consumption is reduced by combining the PWM method and the current value control method to efficiently light the LED according to the image quality mode. be able to.

It is a block diagram which shows the schematic structural example of the liquid crystal display device which concerns on this invention. FIG. 2 is a block diagram illustrating a configuration example of a portion related to an LED backlight in the liquid crystal display device of FIG. 1. It is a figure which shows an example of the PWM Duty table in the LED backlight of FIG. It is a figure which shows an example of the LED current table in the LED backlight of FIG. 3 is a diagram for explaining an example of a light emission luminance control method in the standard mode in the LED backlight of FIG. 2, and a PWM-Duty in the standard mode using the tables of FIGS. 3 and 4 and the LED current control circuit of FIG. 2. It is a figure which shows an example of the relationship between the maximum electric current and brightness | luminance in. It is a figure which shows an example of the forward voltage-forward current characteristic and forward current-relative luminous flux characteristic in LED. It is a figure for demonstrating the other example of the light emission luminance control method in the LED backlight of FIG. It is a figure for demonstrating the other example of the light emission luminance control method in the LED backlight of FIG. It is a figure for demonstrating the other example of the light emission luminance control method in the LED backlight of FIG. It is a figure which shows the other example of the PWM Duty table in the LED backlight of FIG. It is a figure which shows the example of arrangement | positioning of the backlight applicable to the liquid crystal display device of this invention.

  FIG. 1 is a block diagram showing a schematic configuration example of a liquid crystal display device according to the present invention. In addition to the LED backlight 10, the liquid crystal display device 1 includes a tuner unit 11, an operation unit 12, a video signal processing unit 13, a main control unit 14, an LED drive unit 15, an external light illuminance detection unit 16, a liquid crystal control unit 17, and A liquid crystal panel 18 is provided.

  The main control unit 14 directly or indirectly controls the entire liquid crystal display device 1 such as the video signal processing unit 13 and the LED driving unit 15. The part which controls the LED drive part 15 among them is demonstrated as the LED control part 14a. The operation unit 12 only needs to be able to accept user operations and transmit the operation details to the main control unit 14. The operation unit 12 includes a main body operation unit provided as a button or the like on the main body of the liquid crystal display device 1 and an attached remote controller. And a receiving unit that receives the operation signal. Of course, as the operation unit 12, only one of the main body operation unit and the reception unit may be provided.

  The tuner unit 11 is connected to an antenna input terminal of an antenna that receives a broadcast wave, demodulates the broadcast wave input from the antenna input terminal, and outputs the demodulated wave to the video signal processing unit 13. The video signal processing unit 13 performs various signal conversion processes for displaying the video signal input from the tuner unit 11 on the liquid crystal panel 18. By providing the tuner unit 11 and the like, the liquid crystal display device can be configured as a liquid crystal television device.

  In addition, some liquid crystal display devices 1 have an output mode in which the state of video and audio can be set to a user-desired state. For example, a television apparatus is an example. The output mode is also called an AV position or the like, and is also called an image quality mode because the image quality is changed for each output mode.

  As the output mode, for example, “standard mode”, “dynamic mode”, “game mode”, “PC mode”, “AV memory mode”, “movie mode” and the like are set.

  The “standard mode” is a mode indicating that the image quality / audio settings are standard values. The “dynamic mode” is a clear and vivid image that allows sports programs to be viewed as powerful. The dynamic mode can be used as a demo mode (also referred to as a storefront mode) for PR of the characteristics of the device at a storefront of a store, for example. Usually, the dynamic mode is executed with the best image quality and brightness prepared in the video display device.

  The “game mode” is a mode in which video such as a video game is displayed with gentle brightness and is displayed gently on the eyes, and the “PC mode” is a screen mode for PC. The “AV memory mode” is a mode in which arbitrary adjustment contents can be stored for each input. The “movie mode” is a mode in which a signal included in a movie source is extracted as it is, and luminance characteristics and color characteristics are faithfully reproduced with respect to the original signal to express a film feeling.

  The liquid crystal display device 1 according to the present invention has a plurality of image quality modes like the output mode as illustrated, and one image quality mode can be selected from them. The selection of the image quality mode may be performed by a selection operation by the user from the operation unit 12, but the video signal processing unit 13 or the like determines the type and characteristics of the video indicated by the video signal, It may be possible to execute automatically based on this.

  Then, the video signal processing unit 13 performs various types of video processing that match the selected image quality mode and outputs the video processing to the liquid crystal control unit 17.

  The liquid crystal control unit 17 performs control to sequentially write the video signal output from the video signal processing unit 13 from the top line of the liquid crystal panel 18. In the liquid crystal panel 18, vertical scanning is performed by sequentially writing and updating the scanning video signal. The written video signal is held for one frame. By such writing, the video indicated by the input video signal is displayed on the liquid crystal panel 18. At this time, the image is displayed with the image quality of the selected image quality mode.

  The liquid crystal panel 18 is a non-self-luminous panel, and the liquid crystal display device 1 is provided with a light source for irradiating light from the back side in order to view the displayed video. In the liquid crystal display device 1 according to the present invention, the LED backlight 10 is provided as the light source.

  The external light illuminance detection unit 16 includes an OPC (Optical Picture Control) sensor (also called a brightness sensor) that detects the illuminance of external light around the liquid crystal display device 1. The light emission luminance of the LED of the LED backlight 10 can be increased or decreased depending on the illuminance of the ambient light around the liquid crystal display device 1 detected by the OPC sensor. Of course, the external light illuminance detection unit 16 may not be included in the liquid crystal display device 1.

  The main control unit 14 passes the dimming control signal and the mode switching signal to the internal LED control unit 14 a, and the LED control unit 14 a controls the light emission of the LED backlight 10 via the LED driving unit 15.

  The dimming control signal is generated as a signal indicating the dimming setting value based on the result of the brightness adjustment operation (dimming operation) on the operation unit 12 or the detection result on the external light illuminance detection unit 16. The mode switching signal is a signal indicating the image quality mode after switching. That is, as the mode switching signal, a signal indicating a mode corresponding to a mode switching (selection) operation by the user on the operation unit 12 or a type or feature of the video indicated by the video signal is automatically determined based on the video. For example, a signal indicating the determined image quality mode is applicable.

  Next, a configuration example and a control example of the LED backlight 10 will be described with reference to FIGS. FIG. 2 is a block diagram showing a configuration example of a portion related to the LED backlight in the liquid crystal display device of FIG. 3 and 4 are diagrams showing examples of the PWM duty table and the LED current table in the LED backlight of FIG. FIG. 5 is a diagram for explaining an example of the light emission luminance control method in the standard mode in the LED backlight of FIG.

  The relevant part of the LED backlight illustrated in FIG. 2 includes a light emission luminance control unit and an LED backlight (referred to as a backlight unit) 10 having an LED 41. The light emission luminance control unit includes an LED control unit 14 a and an LED drive unit 15.

  The LED control unit 14a controls the light emission luminance of the LED 41 by both the pulse width modulation (PWM) method and the current value control method. The PWM method is a method of changing a duty (hereinafter referred to as a lighting duty) indicating a lighting time per cycle in a pulse for turning on / off the LED 41. Here, the lighting duty D can be expressed by D = τ / T, where T is the lighting / extinguishing cycle of the LED 41 and τ is the lighting period in one cycle. The lighting duty is sometimes called a duty ratio.

  The current value control method is a method of selecting a current value (forward current value) flowing through the LED 41 from a plurality of set values. This set value can also be defined by a voltage value for obtaining the current value.

  In the present invention, at least one of the plurality of setting values is a maximum luminance value used in a specific image quality mode among image quality modes set in the liquid crystal display device 1 (standard in a specific image quality mode). If it is used, it is set to a predetermined current value at which the lighting duty becomes the maximum value at the maximum luminance value specified by the designer. In other words, during this specific image quality mode, the lighting duty is set to the minimum value (the predetermined current value) using the predetermined current value between the predetermined minimum luminance value and the maximum luminance value. Then, the control may be performed so as to gradually increase from the minimum value of the lighting duty for obtaining the minimum luminance value to the maximum value. Hereinafter, the case where the lighting duty is 100% will be described as an example as the maximum value, but any value determined as the maximum value of the lighting duty used in the liquid crystal display device 1 may be used.

  Here, the specific image quality mode is an image quality mode in which the maximum luminance value to be used is smaller than at least the maximum luminance value to be used in another specific image quality mode. In other words, in the liquid crystal display device 1, in addition to the specific image quality mode, an image quality mode in which the maximum luminance value to be used is different and the maximum luminance value to be used can be set can be set. . This larger image quality mode corresponds to the dynamic mode in the above-described example. That is, the specific image quality mode is not a dynamic mode. Of course, even in the dynamic mode, it is preferable to execute such control, that is, control at a current value such that the lighting duty is 100% at the maximum luminance value to be used.

  The specific image quality mode is preferably an image quality mode provided as a mode most used by the user. This image quality mode corresponds to the standard mode in the above example. Hereinafter, an example in which the standard mode is employed as the specific image quality mode will be described. However, the same applies to cases in which other image quality modes are employed.

  A configuration example of the LED control unit 14a that performs such control will be described. The LED control unit 14 a includes a dimming control circuit 23, a PWM signal generation circuit 24, and an LED current control circuit 25. The LED control unit 14 a further includes a memory that stores the PWM duty table 21 and the LED current table 22.

  The PWM duty table 21 includes a plurality of tables as exemplified by the duty table a and the duty table b in FIG. Each table associates a dimming setting value (corresponding to a value changed by user dimming or OPC dimming), a luminance ratio when dimming with each dimming setting value, and a lighting duty. It has been.

  As illustrated in FIG. 4, the LED current table 22 describes a current value used in each image quality mode, and further describes a duty table used in each image quality mode. In this example, the lighting duty is controlled according to the duty table a using I1 as the current value in the dynamic mode, and according to the duty table b using I2 (I2 <I1) as the current value in the standard mode. Controlling the lighting duty is described.

  The dimming control circuit 23 refers to the LED current table 22 and determines a current value and a PWM duty table used for control from the mode indicated by the mode switching signal (or the latest mode switching signal). In addition, the dimming control circuit 23 refers to the determined PWM duty table (table a or table b in this example) in the PWM duty table 21, and controls the dimming control circuit 23 based on the dimming setting value indicated by the dimming control signal. Determine the lighting duty to be used.

  The dimming control circuit 23 outputs the lighting duty determined in this way to the PWM signal generation circuit 24 and outputs the determined current value to the LED current control circuit 25. The PWM duty table 21 and the LED current table 22 are not limited to the description formats as shown in FIGS. 3 and 4, and the current value and the lighting duty for each dimming setting value (or luminance ratio) are different for each image quality mode. If prescribed, for example, even with one table, control by the dimming control circuit 23 is possible. Moreover, although the example which memorize | stores each table 21 and 22 in memory was given, it does not restrict to this, In dimming control circuit 23, each table 21 and 22 is based on the input dimming control signal and mode switching signal. A circuit that can determine the current value and the lighting duty corresponding to the values indicated by, may be adopted.

  The PWM signal generation circuit 24 generates a pulse signal according to the input lighting duty and outputs the pulse signal to the LED drive unit 15. The LED current control circuit 25 generates a current control signal for controlling the current so as to have the input current value, and outputs the current control signal to the LED drive unit 15.

  The LED drive unit 15 includes an LED voltage generation circuit 31 and an LED driver 32. The LED driver 32 outputs a signal for generating an LED drive voltage corresponding to a necessary LED current based on the current control signal input from the LED current control circuit 25. The LED voltage generation circuit 31 outputs a drive voltage to the LED 41 according to the input signal. On the other hand, the LED driver 32 outputs the pulse signal input from the PWM signal generation circuit 24 to the LED 41. Thereby, the LED 41 is applied with the current having the current value determined by the dimming control circuit 23 according to the PWM signal having the pulse width of the lighting duty determined by the dimming control circuit 23, and is turned on / off.

  In this way, the LED control unit 14a drives the LED driving unit 15 while referring to the values of the tables 21 and 22 based on the dimming control signal and the mode switching signal, and the LED driving unit 15 To drive.

  In the present invention, one of the setting values is a current value at which the lighting duty is 100% at the maximum luminance value (in this example, the luminance ratio is 60%) used in the standard mode. This current value is exemplified by I2 in the LED current table 22 of FIG.

When driving with the current value I2, the table b in the PWM duty table 21 in FIG. 3 is used. As a result, the dimming control circuit 23 is controlled in accordance with the dimming control signal, and when controlling at a luminance ratio of 60% or less (in this example, the dimming setting value corresponds to ± 0), the graph of FIG. At 50, the lighting duty is determined according to the relationship indicated by the straight line 51a. In this way, it is possible to control the LED to emit light with the luminance indicated by the straight line 52 (however, the luminance ratio is 60% or less).
In other words, in the standard mode, the current value I2 is fixed and, according to the relationship indicated by the straight line 51a, the lighting duty is controlled to increase toward 100% as the dimming setting value increases.

  A graph 50 in FIG. 5 shows an example of the relationship between the PWM-Duty in the standard mode using the tables in FIGS. 3 and 4 and the maximum current and the luminance in the LED current control circuit 25 in FIG. Here, the current value I2 is indicated by a straight line 53a in the graph 50. Further, in the graph 50, the current is not calibrated and represents only the state of change, and the current value shown in the graph 50 is the maximum current value that can be passed through the LED when the lighting duty is 100%. Point to. About these points, it is the same also about each graph in below-mentioned FIGS. 7-9.

  Next, referring briefly to FIG. 6, it will be briefly described that the control illustrated in FIG. 5 can improve the efficiency of backlight emission and reduce the power consumption. FIG. 6A is a diagram illustrating an example of forward voltage-forward current characteristics in an LED, and FIG. 6B is a diagram illustrating an example of forward current-relative luminous flux characteristics in an LED. Here again, an example is shown in which the standard mode is adopted as the specific image quality mode.

  As in the characteristics shown in FIG. 6B, the relationship between the forward current flowing through the LED and the relative luminous flux (brightness) is a convex function, and the luminous efficiency decreases as the forward current increases. For example, the relative luminous flux is 1.4 at 100 mA, but the relative luminous flux at 200 mA, which is double, is 2.0, which is less than the double. Here, PWM control is not assumed. In other words, FIG. 6B shows characteristics at a lighting duty of 100%. For example, when the lighting duty is set to 50% with the same current value, the lighting duty is 100%. The brightness is almost half that of. For example, if the relative luminous flux at the time of driving at 100 mA and 100% is 1.4, the relative luminous flux at the time of driving at 100 mA and 50% is about 0.7.

  Since the forward current, lighting duty, and brightness have such a relationship, a low current is used to obtain the same brightness (luminance) as when the lighting duty is set to N% (<100%) at a predetermined current value. When the power consumption is compared with the value when the lighting duty is set to 100%, the power consumption is lower when the current value is lowered and the lighting duty is set to 100%. Since the forward voltage and the forward current are in the relationship illustrated in the forward voltage-forward current characteristic of FIG. 6A, the forward voltage of the LED is lowered by the amount of the current value, and the necessary power supply voltage value is Because it goes down.

  A more specific example will be described. In the case of PWM control, for example, the brightness is 2.0 when the lighting duty is 100% at 200 mA, and the lighting duty may be 70% at 200 mA for a brightness of 1.4. Instead, the lighting value may be changed to 100% at 100 mA by changing the current value. It will be described which one has lower power consumption. In FIG. 6A, it is 3.5 V at 200 mA and 3.0 V at 100 mA. Accordingly, when the lighting duty is 70% at 200 mA, 200 mA × 3.5 V × 70% = 490 mW, while at 100 mA, the lighting duty is 100%, 100 mA × 3.0 V × 100% = 300 mW. Therefore, the power consumption is lower when the lighting duty is 100% at 100 mA. As described above, in order to obtain the same brightness, the power consumption becomes lower when the current value is lowered and the lighting duty is set to 100%.

  Referring to the graph 50 in FIG. 5, the relationship between the straight line 51c and the straight line extending to the dark side indicates that the required current value (I1) is indicated by the straight line 53c in the graph 50 when the standard mode is driven. As described above, the current value I2 (current value corresponding to the straight line 53a) at the time of driving with the relationship indicated by the straight line 51a becomes larger, and the voltage necessary for flowing the current value I1 also becomes larger. Therefore, in the present invention, in the standard mode, the current value I2 smaller than the current value I1 is used, and instead, the lighting duty is controlled to be higher than when driving with the current value I1. The current value I2 is a current value for causing the maximum luminance value used in the standard mode to emit light at a lighting duty of 100%.

  Thus, in the standard mode, the power consumption in the standard mode can be reduced by setting the current value so that the lighting duty is 100% at the maximum luminance value used in the standard mode. Therefore, according to the liquid crystal display device 1 of the present invention, when controlling the brightness according to the image quality by combining the PWM method and the current value control method, it is possible to reduce the power consumption for lighting the LED. Further, since control for reducing the luminance is not performed in order to reduce the power consumption, energy saving can be realized without giving the user a sense of incongruity or inconvenience.

  Next, a preferable control example of the LED control unit 14a will be described with reference to FIG. 5 again. The LED control unit 14a needs to change to a luminance value exceeding the maximum luminance value (corresponding to a luminance ratio of 60% in the example of FIG. 5) during operation in the specific image quality mode (that is, with the current value). If it is not possible to control, control is performed using a current value (higher current value) used in another specific image quality mode. This high current value can cope with the above change. Of course, the control is performed using not only the high current value but also the lighting duty value for the dimming set value used in the “other specific mode”. At this time, the video processing in the video signal processing unit 13 may be performed so as to match the image quality mode as it is, and only the brightness control may be performed in the other specific image quality mode.

  In FIG. 5, although the dynamic mode is cited as the other specific image quality mode, the present invention is not limited to this. When the current value I1 used in the dynamic mode is higher than the current value I2 and the brightness is increased to exceed the luminance ratio of 60%, the transition from the straight line 51a to the straight line 51c or the dotted line in the table 21 in FIG. As can be seen from the graph, the lighting duty is once lowered, and the lighting duty becomes 100% at a luminance ratio of 100%. In this way, the LED is controlled so as to emit light with the luminance indicated by the straight line 52 (however, since the straight line 51b described later is ignored here, excluding the luminance ratio of 60% to about 65%). Can do.

  As described above, even when the standard mode is used, the maximum luminance set in the standard mode is required to be exceeded by the user dimming operation by the operation unit 12 or the detection result by the external light illuminance detection unit 16, for example. In such a case, the luminance can be increased without giving the user a sense of incongruity by using the current value in the dynamic mode.

  Such control may be executed not only between the standard mode and the dynamic mode but also in other image quality modes. Thereby, for example, if the liquid crystal display device 1 can set the image quality mode in which the luminance ratio is 40% and the lighting duty is 100%, the standard mode, and the dynamic mode can be set according to the user dimming or the like. As the brightness increases, the lighting duty peak (100%) can be controlled three times. As described above, the lighting duty may be controlled so as to have 3 or more peaks n (lighting duty 100%), and the current value may be switched to n stages.

  Next, the straight lines 51b and 53b in the graph 50 of FIG. 5 will be described. The straight line 51b is a straight line connecting a discontinuous range between the straight line 51a and the straight line 51c (in this example, a luminance ratio of 60% to about 65%). The current value may be calculated in advance from the lighting duty indicated by the straight line 51b, and the current value in the discontinuous range is indicated by the straight line 53b. Thus, by preparing the lighting duty and current value for the straight line 51b as well, it is possible to cope with any of the luminances indicated by the straight line 52 due to user dimming or the like. .

  Moreover, when the LED control part 14a of FIG. 2 changes a current value, it is preferable to change a current value and a lighting duty gradually gradually. At this time, the lighting duty and the current value may be switched simultaneously at an interval of about 0.5 seconds, for example. Such switching can reduce the sense of incongruity given to the user. The change amount of the current value at the time of switching may be, for example, 1 mA per vertical scanning period (for example, 16 ms). In this case, for example, when I1 = I2 + 20 mA, when switching from I2 to I1, 20 vertical scanning periods Will be done at a degree. In particular, in a television apparatus, since an image changes every vertical scanning period, it is preferable to perform switching in this unit.

  In addition, the LED control unit 14a may need to change to a luminance value lower than the maximum luminance value (the maximum luminance value used in the specific image quality mode) during operation in the other specific image quality mode. It is preferable to control using the current value used in the specific image quality mode.

  As an example of the dynamic mode and the standard mode, even in the dynamic mode, it is preferable to control with the lighting duty (and the current value described at the same time) in the relationship such as the straight line 51c and the straight line 51a in FIG. As a result, even during operation in the dynamic mode, power can be saved at a value (for example, a luminance ratio of 65%) or less as compared to controlling the straight line 51c to be extended as it is even at a certain value (for example, a luminance ratio of 65%) or less. Can be achieved.

  Also in this case, when changing the current value, it is preferable to gradually perform the current value and the lighting duty at the same time. Also in this example, the lighting duty is controlled so as to have n or more peaks of 3 times (lighting duty 100%), and roughly speaking (excluding the case of gradually changing), the current value is You may make it switch to n steps.

  Next, various examples of control patterns for emission luminance control applicable to the LED backlight of FIG. 2 will be described with reference to FIGS. 5 and 7 to 9. 7 to 9 all show the relationship among PWM-Duty, maximum current, and luminance.

  The LED has higher power-luminance efficiency as its current value is lower. In the case of a white LED, the color changes slightly depending on the current value. What is necessary is just to decide what control pattern is adopted in consideration of these points. For example, the control pattern may be determined for each installed model or for each image quality mode.

  For example, in the light emission luminance control method described in FIG. 5, the current value (maximum current value in the LED current control circuit 25 in FIG. 2) is changed in several stages, and the lighting duty (PWM control in the PWM signal generation circuit 24 in FIG. 2). This is an example of a control pattern for linearly changing the lighting duty). This control pattern is effective when the current can be switched only in steps. Compared with the case where the current value is fixed at the maximum, the power consumption in the low luminance portion can be suppressed.

  In the graph 50 of FIG. 5, the portion of the straight line 53b corresponds to the transition portion, so that the current value change point is substantially only one point. Therefore, there is only one color change point. Thus, the change point of the current value in this control pattern becomes obvious as the change point of the color. Therefore, it is better to set this change point so that it passes through a limited scene such as user adjustment, not while the user is viewing the content. In addition, since the current value is significantly changed at the current value switching portion, it becomes difficult to control the lighting duty and current timing.

  In the control pattern indicated by the graph 70 in FIG. 7, the lighting duty is changed linearly as indicated by a straight line 71, and the current value is also changed linearly as indicated by a straight line 73. It is changing linearly. In such a control pattern, since both the lighting duty and the current value change linearly, there is no discontinuity and the concept is simple as a whole, but current control and voltage control are always required. The power consumption gradually increases from low luminance to high luminance. In this control pattern, the change in the color of the LED gradually changes, and the color does not change at a stretch at a certain point. Therefore, this control pattern is appropriate as a control pattern while the user is viewing the content.

  In the control pattern shown by the graph 80 in FIG. 8, the lighting duty is increased linearly as shown by the straight line 81a and the lighting duty is 100% as shown by the straight line 81b up to a predetermined luminance (luminance ratio 60% in this example). And After the lighting duty becomes 100%, the current value is linearly increased from the fixed current value indicated by the straight line 83a as indicated by the straight line 83b. In this control pattern, the luminance value is linearly changed as indicated by a straight line 82 by such a change in current value and lighting duty. This control pattern has the lowest current value throughout, and the power consumption can be reduced most from the characteristics of the power-luminance efficiency of the LED. Further, this control pattern is easy to control because only one of voltage control and current control is controlled at each point. In general, since low luminance tends to cause a noticeable change in color, this control pattern can be said to be appropriate control of color by fixing the current value of that portion.

  In the control pattern shown by the graph 90 in FIG. 9, the lighting duty is fixed as shown by the straight line 91a and the current value is changed linearly as shown by the straight line 93a up to a predetermined luminance (in this example, the luminance ratio 53%). Let Then, as shown by a straight line 91b, the lighting duty is linearly increased so that the lighting duty becomes 100% at another predetermined luminance (in this example, 60% in luminance ratio), while the current as shown by a straight line 93b. Decrease the value linearly. From the other predetermined luminance, the current value is fixed at 100% as indicated by a straight line 91c, and the current value is increased linearly as indicated by a straight line 93c. In this control pattern, the luminance value is linearly changed as indicated by a straight line 92 by such a change in current value and lighting duty. The graph 90 shows an example in which the lighting duty is largely switched only once, but the lighting duty can be significantly switched at several stages.

  However, such a control pattern, when trying to change the brightness with a white LED or the like, causes the balance between excitation light and fluorescence to be lost and the spectral pattern to fluctuate if performed directly at a constant current value. Depending on the color, the color may change.

  The control pattern similar to the current control pattern indicated by the straight lines 93a, 93b, and 93c of the graph 90 can be realized by a device that does not perform PWM control (a device that does not include the PWM signal generation circuit 24 in FIG. 2). . Thereby, this apparatus can be made low-cost. In that case, the current value for generating the voltage to be applied to the LED may be switched as shown by the straight lines 93a, 93b, 93c or at several points.

  Next, another example of the PWM duty table in the LED backlight of FIG. 2 will be described with reference to FIG. A PMW duty table 100 illustrated in FIG. 10 is an example of a table used when an AV position and a power saving mode (also referred to as an eco mode) are provided in a liquid crystal panel. In the table 100, the modes other than the standard mode correspond to, for example, a dynamic mode, a game mode, a movie mode, etc. as described above.

  In the table 100, the current value is adjusted depending on whether the eco mode is “off”, “mode 1”, or “mode 2”. In the table 100, the current value when the eco mode is off and the dimming value is the maximum value (16 in this example) is 100%, and other examples of current values are relatively shown. When the dimming value is “16”, the current values when the eco mode is off, mode 1 and mode 2 are 100%, 80% and 60%, respectively.

  As described above, in the example of the table 100, not only the duty is changed according to the dimming value, but also the current value is changed based on the setting content of the eco mode, thereby maintaining the linearity of the luminance change and improving the power efficiency. It is improving. Therefore, power saving can be realized by executing the control exemplified in the table 100.

Further, in the example of the table 100, when the eco mode is off, when the AV position is the standard mode, the current value is switched by the dimming value to save power, and when the mode is other than the standard mode, the current is changed. The value is fixed. Therefore, when the AV position is the standard mode, it is necessary to use a current value corresponding to the dimming value even when the eco mode is on (mode 1 or mode 2). It is set lower than each current value used when the eco mode is off.
Thereby, it is possible to provide the user with a consistent operation without a sense of incongruity.

  In addition, FIG. 10 shows an example of values assuming that the duty luminance characteristics are constant at each current value, but when the duty luminance characteristics change at each current value, a duty table is set for each current value. Just keep it.

  FIG. 11 is a diagram showing an example of the arrangement of the backlight applicable to the liquid crystal display device of the present invention. The LED backlight 10 whose arrangement is illustrated in FIG. 11 is configured as an array type LED backlight. However, the liquid crystal display device of the present invention is not limited to the example described here, and a matrix type LED backlight or the like in which LEDs are laid on a substrate having the same size as the screen can be mounted.

  The LED backlight 10 includes a plurality of LED substrates 101 on which a plurality of white LEDs 102 are mounted on a chassis 105. The LED substrate 101 has a horizontally long rectangular strip shape, and is arranged such that the longitudinal direction of the rectangle coincides with the horizontal direction of the screen of the liquid crystal display device. Further, a harness 103 is provided to connect the LED boards 101 divided in two in the horizontal direction, and a harness 104 is provided to connect one LED board 101 and an external driver board. Further, a connector 106 to which the harnesses 103 and 104 are connected is installed on each LED board 101. In the liquid crystal display device according to the present invention, the division in the horizontal direction of the LED substrate 101 as illustrated in FIG. 11 is not essential.

DESCRIPTION OF SYMBOLS 1 ... Liquid crystal display device, 10 ... LED backlight (backlight part), 11 ... Tuner part, 12 ... Operation part, 13 ... Video signal processing part, 14 ... Main control part, 14a ... LED control part, 15 ... LED drive , 16 ... External light illuminance detection unit, 17 ... Liquid crystal control unit, 18 ... Liquid crystal panel, 21 ... PWM duty table, 22 ... LED current table, 23 ... Dimming control circuit, 24 ... PWM signal generation circuit, 25 ... LED current Control circuit 31 ... LED voltage generation circuit 32 ... LED driver 41 ... LED 50 ... graph 51a, 51b, 51c ... straight line 101 ... LED substrate 102 ... LED 103,104 ... harness 105 ... chassis 106: Connector.

Claims (5)

In a liquid crystal display device having a liquid crystal panel that displays an input video signal, a light source of a light emitting diode that illuminates the liquid crystal panel, and a light emission luminance control unit that controls the light emission luminance of the light emitting diode,
The light emission luminance control unit includes a pulse width modulation method for changing a duty indicating a lighting time per cycle in a pulse for turning on / off the light emitting diode, and a current value flowing through the light emitting diode from a plurality of set values. Control the light emission brightness of the light emitting diode in both the current value control method to be selected,
At least one of the plurality of setting values is a maximum luminance value used in a specific image quality mode among image quality modes set in the liquid crystal display device, and a predetermined current value at which the duty becomes a maximum value. Yes,
The liquid crystal display device, wherein the specific image quality mode is an image quality mode in which the maximum luminance value to be used is smaller than at least the maximum luminance value to be used in another specific image quality mode.   2. The liquid crystal display device according to claim 1, wherein the specific image quality mode is an image quality mode provided as a mode most used by a user.   3. The liquid crystal display device according to claim 1, wherein the light emission luminance control unit is configured to change the other when a luminance value exceeding the maximum luminance value needs to be changed during operation in the specific image quality mode. A liquid crystal display device controlled by using a current value used in a specific image quality mode.   4. The liquid crystal display device according to claim 3, wherein the light emission luminance control unit, when operating in the other specific image quality mode, needs to be changed to a luminance value lower than the maximum luminance value, A liquid crystal display device controlled by using a current value used in an image quality mode.   5. The liquid crystal display device according to claim 3, wherein the light emission luminance control unit gradually changes the current value and the duty simultaneously when changing the current value.

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